Effect of triphenyl tetrazolium chloride staining on the distribution of radiolabeled pharmaceuticals

Myocardial tissue is routinely exposed to the vital stain triphenyl tetrazolium chloride (TTC) to delineate infarction in conjunction with myocardial isotope research. However, it is unknown whether TTC has a direct effect on tracer deposition. We evaluated this possibility in rabbit hearts injected with either teboroxime, sestamibi or 201Tl. The hearts were excised and treated as follows: (1) TTC or normal saline was perfused through the heart and the residual activity monitored; (2) hearts were sliced into 0.5-cm thick sections, counted and incubated in either TTC or normal saline for 10 min then recounted; and (3) the circumflex artery was ligated postmortem and TTC perfused. Autoradiographic images were produced from 30-microns slices to depict any disparity in activity concentration from the selective perfusion of TTC. Both perfusion and incubation by TTC resulted in a significant activity loss of both 201Tl and sestamibi, but not teboroxime, compared to normal saline. An independent octanol extraction experiment measured the change in the partition coefficient of labeled teboroxime and sestamibi induced by the addition of TTC. TTC was shown to liberate the radiolabel from sestamibi, but not from teboroxime. We conclude that histochemical staining techniques involving TTC can alter the distribution of radiolabeled pharmaceuticals. As a result, experiments using TTC with 201Tl and sestamibi should be interpreted cautiously.